Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the alimentary tract rarely observed in children. The treatment of choice for GIST is surgical resection. Although the prognosis of GISTs with low malignant potential is excellent, high-malignant- potential GISTs have a high rate of recurrence. Prognostic factors such as tumor size, mitotic rate and presence of metastases may provide an indication for adjuvant imatinib mesylate (IM) treatment. Here we present a young patient with a large GIST with high-risk features who is in complete remission after surgical excision and adjuvant IM treatment. This patient is the only colon-located CD117-positive case where IM was administered. The exact indications as well as the optimal dose and duration of IM need to be clarified with the contribution of new cases and the growing experience of this rare disease. © Il Pensiero Scientifico Editore.